Conventional display devices basing on LCD and CRT technology can display images with maximum luminance contrast of 1:400, while the human eye can capture luminance ranging from 10−4 to 108 cd/m2 through mechanisms of visual adaptation. High luminance contrast enhances quality of the video and is necessary to achieve realistic appearance of a reproduced scene. Since display devices capable of showing images with a contrast of 1:105 are becoming available, there is a need for an efficient storage and transmission of large amounts of visual information contained in high dynamic range (HDR) video.
Today's state of the art technology enables acquisition and presentation of high-dynamic range images and video. However, to utilize a complete HDR pipeline from acquisition to display, efforts are made to reach efficient storage and transmission of HDR video. Existing image compression methods and apparatus allow for storage of the video that is meant to be displayed only on said conventional display devices (e.g. CRT, LCD), i.e. low dynamic range (LDR) video.
On the acquisition side, several HDR video cameras have become available on the market in recent years: Autobrite from SMal Camera Technologies, HDRC from IMS Chips, LM9628 from National, and Digital Pixel System from Pixim. The HDR range video can also be captured using inexpensive, traditional low dynamic range (LDR) cameras. In Kang et al., 2003, “High Dynamic Range Video”, ACM Transactions on Graphics, volume 22, number 3, pages 319-325 it is shown that registered video frames, which are captured with quickly changing exposures, can be fused into HDR frames. Also, sensors used in surveillance, remote sensing, space research, and medical applications (e.g. CT scanning) produce HDR images and video. Another source of HDR video are computer simulations, common in the global illumination computation and scientific visualization.
Recently, HDR display devices have become available as well. Those enable direct displaying of HDR video with luminance ranges of 0.01-10,000 cd/m2. However, what is even more important, traditional LDR display devices can benefit from HDR video streams as well. HDR video contains complete information that the human eye can register and the so-called tone mapping techniques can use this information for displaying video in an optimal way by taking into account the state of HVS adaptation. This way the video reproduction can be dynamically adapted to any external lighting conditions and customized for any type of a display device (projector, plasma, CRT, LCD) and its unique characteristics. Such customization is not possible by the means of current LDR video technology because of missing luminance information, which leads to unnecessary lower visual quality of video reproduction.
Since the number of applications utilizing HDR technology is rapidly increasing and steady progress in the development of HDR capable capture and display devices is observed, there is a need for an efficient storage and transmission of large amounts of visual information contained in HDR video. The efficient storage and transmission of such HDR data is crucial for the completeness of any HDR imaging pipeline. Existing image compression methods and apparatus allow for storage of the LDR video, with limited information that is optimized to be displayed on only typical display devices.
An important problem is the HDR image encoding which usually relies on the luminance and color gamut quantization for storage and transmission efficiency. Some successful attempts have been made to develop compression methods for static HDR images. Bogart et. al. “OpenEXR image file format”, ACM Siggraph 2003, Sketches & Applications show the successful encoding for still HDR images, but no efficient inter-frame encoding of HDR video.
Therefore it is seen to be desirable to provide a method and apparatus for encoding HDR video, which are capable to reproduce the appearance of images as perceived by a human observer in the real world by providing an efficient storage and transmission method of large amounts of visual information contained in HDR video.